[PATCH v1 4/4] usb: serial: mxuport: add sysfs control for UART FIFO

Crescent Hsieh
2026-03-24T03:51:38Z

Add a per-port sysfs attribute, uart_fifo, to allow userspace to enable
or disable the UART FIFO at runtime.

Map the requested state to the RQ_VENDOR_SET_FIFO_DISABLE vendor command
and track the current FIFO setting in the per-port private data.

Initialize the FIFO state during port probe and remove the sysfs
attribute when the port is released.

Signed-off-by: Crescent Hsieh <crescentcy.hsieh@moxa.com>
---
drivers/usb/serial/mxuport.c | 75 ++++++++++++++++++++++++++++++++++++
1 file changed, 75 insertions(+)

diff --git a/drivers/usb/serial/mxuport.c b/drivers/usb/serial/mxuport.c
index 9a8bb4f02da3..24b86d1a31d4 100644
--- a/drivers/usb/serial/mxuport.c
+++ b/drivers/usb/serial/mxuport.c
@@ -183,6 +183,7 @@ struct mxuport_port {
u32 hold_reason;
u8 mcr_state; /* Last MCR state */
u8 msr_state; /* Last MSR state */
+ bool fifo_enabled;
struct serial_rs485 rs485;
struct mutex mutex; /* Protects mcr_state */
spinlock_t spinlock; /* Protects msr_state */
@@ -1242,6 +1243,68 @@ static int mxuport_probe(struct usb_serial *serial,
return err;
}

+static ssize_t uart_fifo_show(struct device *dev, struct device_attribute *attr,
+ char *buf)
+{
+ struct usb_serial_port *port = to_usb_serial_port(dev);
+ struct mxuport_port *mxport = usb_get_serial_port_data(port);
+
+ if (mxport->fifo_enabled)
+ return sysfs_emit(buf, "enabled\n");
+
+ return sysfs_emit(buf, "disabled\n");
+}
+
+static ssize_t uart_fifo_store(struct device *dev,
+ struct device_attribute *attr,
+ const char *buf, size_t count)
+{
+ struct usb_serial_port *port = to_usb_serial_port(dev);
+ struct mxuport_port *mxport = usb_get_serial_port_data(port);
+ struct usb_serial *serial = port->serial;
+ bool state;
+ int ret;
+
+ if (!count)
+ return -EINVAL;
+
+ ret = kstrtobool(buf, &state);
+ if (ret < 0)
+ return ret;
+
+ if (state == 1) {
+ ret = mxuport_send_ctrl_urb(serial, RQ_VENDOR_SET_FIFO_DISABLE,
+ 0, port->port_number);
+ if (ret)
+ return ret;
+
+ mxport->fifo_enabled = true;
+ } else if (state == 0) {
+ ret = mxuport_send_ctrl_urb(serial, RQ_VENDOR_SET_FIFO_DISABLE,
+ 1, port->port_number);
+ if (ret)
+ return ret;
+
+ mxport->fifo_enabled = false;
+ } else {
+ return -EINVAL;
+ }
+
+ return count;
+}
+static DEVICE_ATTR_RW(uart_fifo);
+
+static int mxuport_create_sysfs_attrs(struct usb_serial_port *port)
+{
+ return device_create_file(&port->dev, &dev_attr_uart_fifo);
+}
+
+static int mxuport_remove_sysfs_attrs(struct usb_serial_port *port)
+{
+ device_remove_file(&port->dev, &dev_attr_uart_fifo);
+
+ return 0;
+}

static int mxuport_port_probe(struct usb_serial_port *port)
{
@@ -1266,18 +1329,29 @@ static int mxuport_port_probe(struct usb_serial_port *port)
if (err)
return err;

+ mxport->fifo_enabled = true;
+
/* Set transmission mode (Hi-Performance) */
err = mxuport_send_ctrl_urb(serial, RQ_VENDOR_SET_HIGH_PERFOR,
0, port->port_number);
if (err)
return err;

+ err = mxuport_create_sysfs_attrs(port);
+ if (err)
+ return err;
+
/* Set interface (RS-232) */
return mxuport_send_ctrl_urb(serial, RQ_VENDOR_SET_INTERFACE,
MX_INT_RS232,
port->port_number);
}

+static void mxuport_port_remove(struct usb_serial_port *port)
+{
+ mxuport_remove_sysfs_attrs(port);
+}
+
static int mxuport_attach(struct usb_serial *serial)
{
struct usb_serial_port *port0 = serial->port[0];
@@ -1501,6 +1575,7 @@ static struct usb_serial_driver mxuport_device = {
.num_bulk_out = 1,
.probe = mxuport_probe,
.port_probe = mxuport_port_probe,
+ .port_remove = mxuport_port_remove,
.attach = mxuport_attach,
.release = mxuport_release,
.calc_num_ports = mxuport_calc_num_ports,
--
2.43.0